Valve operating mechanism

Abstract

A valve operating mechanism for an internal combustion engine having a plurality of exhaust valves per cylinder comprises a device for driving the exhaust valves in a same cylinder at such a valve timing that makes opening of the exhaust valves with a phase difference, i.e., at different timings relative to a crank angle. In one aspect of this invention, the exhaust valves open at the different times and close at the same time.

What is claimed is: 
     
       1. A valve operating mechanism for an internal combustion engine having a plurality of exhaust valves per cylinder, comprising: means for driving at least one of said exhaust valves at a variable valve timing and lift than remainder said exhaust valves in a same cylinder; and   means for controlling said driving means so as to vary the valve timing and lift of said at least one exhaust valve in accordance with variations in operating condition of said engine.   
     
     
       2. A valve operating mechanism for an internal combustion engine having a plurality of exhaust valves per cylinder, comprising: means for driving said exhaust valves at such a valve timing that makes said exhaust valves in a same cylinder start opening at different times and fully close at the same time.   
     
     
       3. A valve operating mechanism as set forth in claim 2 wherein said engine comprises two exhaust valves per cylinder, and closing movements of said exhaust valves are performed at the same speed. 
     
     
       4. A valve operating mechanism as set forth in claim 3 wherein said exhaust valves effect a valve overlap together with a intake valve of said engine. 
     
     
       5. A valve operating mechanism as set forth in claim 2 wherein said engine has three exhaust valves per cylinder, and closing movements of said exhaust valves are performed at different speeds. 
     
     
       6. A valve operating mechanism as set forth in claim 5 wherein said exhaust valves effect a valve overlap together with an intake valve of said engine. 
     
     
       7. A valve operating mechanism for an internal combustion engine having a plurality of exhaust valves per cylinder, comprising: means for driving said exhaust valves in a same cylinder at such a valve timing that makes said exhaust valves open and close at the same time and at different opening speeds so as to effect different maximum valve lifts.   
     
     
       8. A valve operating mechanism as set forth in claim 7 wherein said exhaust valves effect a valve overlap together with an intake valve of said engine. 
     
     
       9. A valve operating mechanism for an internal combustion engine having two exhaust valves per cylinder, comprising: first drive means for driving one of said exhaust valves at a fixed valve timing and lift;   second drive means for driving the other of said exhaust valves in a same cylinder at a variable valve timing and lift; and   control means for controlling said second drive means so as to vary said valve timing of said other exhaust valve in accordance with variations of operation of said engine.   
     
     
       10. A valve operating mechanism as set forth in claim 9 wherein said fixed valve timing and lift makes said one exhaust valve effect a first valve overlap with an intake valve of said engine, and said control means makes said second drive means drive said other exhaust valve at the same valve timing and lift as said one exhaust valve during high speed operation of said engine, at a second valve timing and lift that makes said other exhaust valve open in retard of the time when said one exhaust valve opens, closes in advance of the time when said one exhaust valve close and effect a maximum valve lift smaller than that of said one exhaust valve so that said other exhaust valve fully closes prior to opening of said intake valve during middle-speed high-load operation of said engine, and at a third valve timing and lift which is substantially intermediate between said first and second valve timings and lifts and makes said other exhaust valve effect a predetermined valve overlap during low to middle speed operation of said engine other than said middle-speed high-load operation of said engine. 
     
     
       11. A valve operating mechanism as set forth in claim 10 wherein said middle-speed high load operation of said engine corresponds to an operation range of said engine in which a drop of output torque occurs due to back flow pressures. 
     
     
       12. A valve operating mechanism as set forth in claim 9 wherein said fixed valve timing and lift makes said one exhaust valve effect a first valve overlap together with an intake valve of said engine, and said control means makes said second drive means drive said other exhaust valve at the same valve timing and lift as said one exhaust valve during high speed operation of said engine, at a second valve timing and lift that makes said other exhaust valve open in retard of the time when said one exhaust valve opens, close in advance of the time when said one exhaust valve close and effect a maximum valve lift smaller than that of said one exhaust valve so that said other exhaust valve fully closes prior to opening of said intake valve during particular middle operation of said engine, and at a third valve timing and lift which is substantially intermediate between said first and second valve timings and lifts and makes said other exhaust valve effect a predetermined valve overlap during low to middle speed operation of said engine other than said particular middle-speed operation of said engine. 
     
     
       13. A valve operating mechanism as set forth in claim 12 wherein said particular middle-speed operation of said engine corresponds to an operation range of said engine in which a drop of output torque occurs due to back flow pressures.